Pressure-medium operated friction clutches, as they are known in various designs, cannot be used for the above-mentioned purpose, because the starting and turning-off operations must occur independently dependent on the turbine and/or engine speed in order to avoid additional control devices. Also mechanically shiftable friction clutches, which meet the demands of the specific application are not known.
Therefore the basic purpose of the invention is to provide a clutch for the purpose mentioned above.
The purpose is attained by providing a friction clutch having friction members therein which, depending on the speed of the engine and/or the speed of the turbine, automatically closes in the direction of engagement and opens in the direction of disengagement, with the friction members being compressible in direction of engagement against the force of a spring member by a piston of a rotating cylinder-piston-unit provided on a drive side of the clutch, a fluid being provided and conveyed by an external pumping device into a cylinder applying in response to rotation a pressure onto the piston. That is, the supplied fluid applies a pressure onto the piston under the action of centrifugal force in the cylinder rotating dependent on the turbine speed, which pressure compresses the friction members against the force of the spring. When the turbine speed drops and the pressure of the fluid decreases, the clutch is again opened by the spring.
An advantageous embodiment is where the cylinder is connected to a driving element, namely, the output shaft of the turbine and is designed with an annular chamber therein for receiving the piston therein and is supported rotatably on a shaft arranged on a driven side of the clutch. Using the motor lubricant as the fluid for the clutch is very advantageous because no additional closed fluid circuit is needed for the operation of the clutch. The pump, which is provided anyway, supplies also the clutch with oil. Since the pressure of the supplied engine lubricant is not constant and since the cylinder has only a limited volume in which a pressure dependent on the turbine speed is to build up, a relief bore is provided through which all oil not needed for the pressure build-up is discharged or through which a lubricant pressure, which may possibly be too high, is reduced.
The piston is advantageously secured against an unintentional rotation. A limited relative rotation between the piston and the cylinder can thereby be utilized to interrupt the fluid supply in response to the speed on the driven side of the clutch being higher than the speed on the driving side of the clutch. This provides an overload safety measure for the turbine should there occur a sudden speed increase of the engine, for example, during down-shifting on an incline. An advantageous further development of the clutch includes the provision of at least one curved groove which is covered toward the annular chamber by a disk or the like resiliently resting on the piston. The resilient cover of the groove permits the fluid in the groove to escape only slowly during the relative rotation between piston and cylinder, which avoids a sudden opening and closing of the clutch.
A further development of the clutch which includes a device for interrupting the fluid supply at a low speed of said engine (idling speed) is sensible in order to uncouple the turbine from the engine during idling of the engine, even if the clutch is still closed. This is particularly sensible during a sudden speed reduction of the engine, for example, when the vehicle driver's foot slips off from the clutch pedal. An advantageous embodiment for a device for effecting an uncoupling of the turbine from the engine in such cases is through an interruption of the fluid supply to the clutch. Since a 100% seal cannot be achieved with simple structure, a further relief bore is advisable. Since only leakage oil needs to be discharged and the pressure build-up in the cylinder must be assured during normal fluid supply, this bore is to have only a very small cross section.
To protect the clutch against vibrations (rotational irregularities) coming from the engine, which vibrations are very high particularly in the lower speed range of the engine, an attenuating or damping member is provided between the clutch and a crankshaft of the engine. The attenuating or damping member (vibration attenuator) does not need to be integrated into the clutch, but can also be arranged separately from the clutch, for example, within a transmission step or between two transmission steps, which is or are arranged between the clutch and the crankshaft of the engine.
To achieve a satisfactory start of the closing operation without any delays, a further development includes the provision of plural friction members, each of which include friction surfaces which rest with little pressure on one another, also when said clutch is disengaged. One very simple design includes at least one spring for pressing the disk against the piston to cause initial contact of the friction surfaces. To limit the maximum transmittable torque, the path covered by the piston during engagement is limited by a stop.